Automatic telephone system



.1. M.IBLACKHALL 2,396,077 AUTOMATIC- TELEPHONE SYSTEM March 5, 1946.

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AUTOMATIC TELEPHONE SYSTEM Filed Sept. 29, 1943 13 Sheets-Sheet 13 IN V EN TOR. rfamias' M Black/bald Patented Mar. 1946 AUTOMATIC TELEPHOH E SYSTEM- James M. Blackhall, Genoa, 111., assignor to Lelch Electric Company, Genoa, Ill., a corporation of Illinois Application September 29,1943, Serial No. 504,246

' 10 Claims.

The present invention relates in general to automatic telephone systems and more in particular to new and improved switching apparatus and circuits for use in such systems.

As indicating generally the type'of system and apparatus to which the invention relates, reference maybe madeto the U. S.patent to Boswau, No. 2,307,757, granted January 12, 1943. The invention may be considered as an improvement on and ,further development of the system and apparatus disclosed in the Boswau patent.

The switching apparatus disclosed in the Boswau patent is a special type of what is commonly referred to as cross-bar switching apparatus. The principal object of the invention is to produce a new and improved switching apparatus of this character. While retaining the essential advantages of this type of apparatus, a considerable number of improvements are incorporated which are valuable from the standpoint of manufacture 'and operation, and which increase the flexibility of this type of apparatus and facilitate the maintenance thereof.

The invention and various features thereof will be described morefully hereinafter with reference to the accompanyingdrawlngs, in which- Fig. 1 is a diagrammatic representation of a complete cross-bar switching-mechanism constructed inaccordance with theinvention, showing the principal parts of which the mechanism is composed;

Fig. 2 is a partial front view of the above, showing the No. l trunk unit and the selection control unit, the intervening trunk and test units being omitted;

Fig. 3 is a rear view of the same twounits shown in Fig. 2;

Fig. 11 is a plan or top view of the tens armature yoke;

Fig. l2'is a side view of the units armature yoke;

Fig. 13 is a partial plan view of the same;

Fig. 14 is a plan or top view of the units auxil-' iary armature yoke;

Fig. 4 is a view of the No. l trunk unit, as seen I from the left in Figs. 1 and 2;-

Fig. 5 is a vertical-section between the first and second trunk units, Fig. 1, showing the No. 'l trunk unit as seen from the" right in Figs. 1 and 2; Y

Fig. 6 is a view of the selection control unit, as

seen from the right in Fig. 1' or Fig. 2:

Fig. '7' shows a trunk unit frame and trunk op erating magnet;

Fig. 8 is a top'view of a trunk unit frame, with the operating magnet removed;

Fig. 9 shows-the selection control'unit frame, with the tens and units, selector bar operating magnets and'the tens solenoids;

Fig. 10 is a top view of thev selection control unit frame,'with the operating magnets and solenoids removed;

Fig. is a side view of the same;

Fig. 16. is a partial side view of the tens armature yoke, with attached supporting plate;

Fig. 17 is a schematic view of a portion of the bank at the test unit and adjacent trunk unit,

showing the terminal connections for the line bars;

Fig. 18 is a plan view of one of the line bar supporting plates;

Fig. 19. is a section on the line Ill-l9, Fig. 18;

Fig. 20 is a section on the line 2020, Fig. 18;

. Fig. 21 is a plan or top view of one of the intermediate trunk elements;

Fig. 22 is a section on the line 22-22, Fig. 21;

Fig; 23 is a section through a portion of the bank showing the arrangement for retaining an intermediate trunk element in assembled position on a line bar, supporting plate;

Figs. 24 and 25 are side and edge views, respectively, of one of the tens actuator bars;

Fig. 26 is a front view of one of the units actuators and associated parts, including the spring clutch;

Fig. 2''! is a section on the line 21-21, Fig. 26;

Fig. 28 is a section on the line 28-28, Fig. 26;

Fig. 29 shows the spring clutch and associated parts for operating a tens actuator bar;

Fig. 30 is a section on the line 30-30, Fig. 29;

Fig. 31 shows the spring clutch housing as seen larger scale certain parts shown in Fig. 32;

Fig. 34 is a partial section showing the arrangement for coupling a tens selector bar to the associated core member of the magnetic clutch;

Figs. 35 and 36 are sectional views showing further details of the coupling arrangement; and --'Fig. '37 is a diagrammatic circuit drawing, showing suitable circuits for the switching mechanism when used to perform the functions of.

finder switches in an automatic telephone system.

Thejswitching apparatus or mechanism shown in Fig. 1 comprisesa base II, on which there are supported a plurality of trunk units such as I2, a test unit I3, and a selection control unit I4. The test unit I3 and the selection control unit I are common to all the trunk'units, of which there may be any desired number. Nine trunk units are shown in the drawings numbered from I to 9, which is the full capacity of the base shown. The base need not be fully equipped, however, and.,a smaller number of trunk units could be supplied, say six or seven, the rest to be added as required. On the other hand, a longer base can be provided, having a capacity of fifteen or more trunk units in addition to the test and selection control units. It will be understood from the foregoing that the trunk units are individually removable and replaceable.

As shown in Fig. l, the test unit I3 is located adjacent the selection control unit, I4. The test unit may, however, be located at any point to the left of the selection control unit. It may, for example, be located at the extreme left of the switching mechanism in the position occupied by the No. I trunk unit.

The complete switching mechanism shown in Fig. 1 has a capacity of 100 lines and nine trunk lines, although the number of trunk lines in variable, as will be understood from the preceding paragraphs. As described herein the switching mechanism is arranged for use as a group of finder switches, for connecting calling subscribers lines to idle trunk lines, but it may also be used to perform the functions of selector or connector switches.

There are 300 conductors in the form of bars extending lengthwise of the switching mechanism through the trunk units and the test unit. Since there are three bars per line, two line bars and a test bar, the 300 bars constitute 100 sets of bars and provide terminal facilities for 100 lines, .as indicated above. When the switching mechanism is used to perform the functions of finder "switches it handles the outgoing calls from a group of 100 subscribers lines, which are connected to the line bars in the 100 sets of bars, respectively.

Each trunk unit is individual to an outgoing trunk line terminating therein and includes switching means for connecting any subscribers line to such trunk line. For this purpose the subscribers lines. are divided into ten sub-groups of ten lines each; and each trunk unit is equipped with ten intermediate trunk lines, together with circuit closing means whereby the subscribers lines of any sub-group may be connected to the intermediate trunk lines and whereby any intermediate trunk line may be connected to the outlines each, or ten subgroups of six lines each. The physical grouping of the sets of bars corresponds to the grouping of the lines, and the selector bars and associated equipment corresponding to unused tens and units digits may be omitted. Thus, if there are only six sub-groups going trunk line terminating in such trunk unit.

Y parts beneath.

For controlling the operation of the circuit closing means in the trunk units two sets'of selector bars are provided There are ten tens selector bars and ten units selector bars, all of which extend lengthwise of the switching mechanism and are common to all the trunk units. These selector bars are controlled and operated from the selection control unit at the end. The test unit cooperates in the control of the units selector bars.

It will be understood, of course, that in the case of a small exchange having less than 100 lines, the switching mechanism need not be fully equipped. In a -line exchange, for example, the switching mechanism requires only sixty sets of bars, or 180 bars altogether. The subscribers lines may be divided into six sub-groups of ten only six tens selector bars are required, whereas if there are only six lines per sub-group only six units selector bars are required. The latter arrangement is generally to be preferred since it requires only six intermediate trunks instead of ten.

The foregoing will be suflicient to give a general idea of. the construction of the switching mechanism and the functions which it is adapted to perform. Further details will be supplied hereinafter.

The first or No. I trunk unit shown in Fig. 1 will now be described. The various parts of the trunk unit are mounted on a frame the shape of which will be understood from Figs. 2 to 5, inclusive, with the aid of Figs. 7 and 8, the latter drawings showing two views of the bare frame before any of the parts except the trunk operating magnet have been assembled thereon. The frame is preferably cast from an aluminum alloy, and is in three parts, consisting of the frame proper and two extensions at the top for supporting the trunk operating magnet. The frame proper comprises the two vertical side members 20 and 2I and the horizontal members 23 and 22 which connect the' side members together at the top and bottom, respectively. The horizontal member 22 at the bottom is in alignment with the vertical side members 20 and 2I, as can be seen in Fig. 8. This figure and Figs. 2 and 3 show the two foot members 24 and 25 which rest on the base II. The horizontal member 23 is located between the ends of projecting portions of the frame which extend to the right in Fig. 2 and can be seen in Fig. 5.

The frame extensions referred to are indicated by reference numerals 26 and 21, and are received in recesses at the top of the frame proper where they are held by screws as indicated. The trunk operating magnet comprises the core 28,

the coil or winding 29 and the two pole pieces 30,

and 3|, and is supported on the extensions 26 and 21 as shown. The two pole pieces may have holes drilled therein to receive the core, on which they are held by a press fit. The screws 32 and 33 pass through the extensions 26 and 21, respectively, and are threaded into the ends of the core 28. The smaller screws 34 and 35 are threaded into the pole pieces and assist in holding the magnet in position. The magnet assembly, including the two frame extensions, is removable as a unit for repair or to give access to The frames of all the trunk units are alike. The frame of the test unit is the same as the trunk unit frames.

The selection control unit frame can be seen in Fi s. 2, 3 nd and also in Figs. 9 and 10. Like the trunk unit frame the control unit frame consists of a frame proper and two extensions on which the operating magnets are mounted. The frame proper includes the two vertical members 40 and ll, which are located at the left as the frame is seen in Fig. 2. At the bottom these vertical members are connected by the horizontal member 42. Projecting to the right from the lower ends of the vertical members 40 and 4| are the foot members 43 and 44, which rest on the base II. At the top there are corresponding projecting members 45 and 48. The root member 44 and the projecting member 48 in vertical alignment therewith, which can be seen clearly inthe rear view, Fig. 3, are somewhat longer than the corresponding parts 43 and 45, Fig. 2, and

are provided at the ends with rounded offset portions 41 and 48 for receiving .the pivot screws for 45 and 48- are connected by a horizontal shelf 49, on which the tens solenoids are mounted. Extending between the projecting member 45 and the foot member 43 there is a web 50 on which the units solenoids are mounted.

The extensions i and 52 are clearly shown in the several flguresand will require no detailed description. They are secured to the frame by screws, as indicated, lapped Joints being used which are similar to the joints used at the trunk unit frames. At the top the extensionsil and 52 support the tens operating magnetcomprising the core 54, the 'winding 53 and the two pole pieces 55 and 56. Below the tens operating magnet is the units operating magnet comprising the core 58, the winding 51, and the two pole pieces. 59 and 60. These magnets are mounted the same as the trunk operating magnet previously described. It will be clear also that the assembled extensions and magnets constitute a unit which can be removed from the frame for repairs or any other purpose.

The trunk unit frames, test unit frame and the selection control unit frameare supported close together on the base I I, as indicated in Fig. l, the space allotted to each frame being determined by the length of the footmembers such as 24 and 25 of the No. l trunk unit. Referring to Fig. 2, for example, it will be understoodthat in practice the No. 2 trunk unit is mounted just to the right of the No. l trunk unit shown, with the back of the frame. of the No. 2 unit in contact with the ends of the foot members 24 and 25 of the No. I unit frame. The extensions such as 21 of the frames are also in contact and are held together by a link 61, similar links being used between each two adjacent frames. The frames of all the units are attached to the base I i by means of screws, as shownclearly in the several. figures of .the drawings 2 to 6, inclusive.

It will be convenient now to explain the construction of the bank comprising the line and test bars, intermediate trunk elements, and outgoing.

trunk elements, these parts constituting the ciredit-closingmeans for connecting calling subscribers lines with outgoing trunk lines.

As mentioned previously, there are 100 sets of bars, each set comprising two line bars and a test bar, or 300 bars in all. There could, of course, be

Each line or test bar is a continuous metallic strip about one-eighth of an inch in width and long enough to extend through all the trunk units and the test unit. The length will accordingly vary with the trunk capacity of the switch mechanism. The bars or strips maybe made of any suitable material, but preferably are of stainless.

steel.

The line and test bars are supported at the No.

able "plastic such as polystyrene, and its length is equal to the width 01' the trunk unit frame.

Countersunk holes 62 at one end and 83 at the.

other end are provided for screws by means of which it is attached to the vertical side members of the frame. The plate BI is also provided with six rows of. tapered rectangular openings such as-64, there being .ten'such openings in each row.

These'openings are for receiving the line and test bars. Beneath each row of openings '64 there is a groove'85. The tapered shape of the openings '64 will be clear from Fig. 20, also Figs. 4 and 5. Five plates such as 6| are required, since there are 300 line and test bars and each plate accommodates 60 bars. The plate BI is the top plate and is attached to the vertical side members 20 and 2| of the trunk unit frame by means'oi' four screws 61 which pass through the countersunk holesBZ and 53 in the plate and are-threaded pear lnFig. 5, but the two screws at the other end of the plate are obscured by other parts. It will be noted that plate 6| is assembled to the frame with the grooved side to the right and with .the large ends of the tapered openings to the left, as the trunk unit is seen in Fig. 2. This is apparent from Figs. 4 and 5 which show the trunk unit as seen from the left and right, respectively.

The other four plates are assembled on the frame below plate 6!, as will be understood from Figs. 4 and 5. Only two complete plates are shown and parts of two other plates, but it will be understood that there are flve plates altogether, as is required to take care of the 300 bars.

As seen clearly in Fig. 4, for example, the holes in theplates at the several units are in horizontal.

and vertical alignment.

Five plates such as 6| are also carried on the "frame of the selection control unit, as can be seen from Figs. 2 and 3. where the top plate is indicated at 6|. At the selection control unit the plates carry the terminals for the line and test bars. The construction of the terminals is shown clearly in Fig; 1'7. The upper terminal, for example, comprises two flexible metal strips 69 and 10, having curved jaws 'II and 12 formed as shown. "The fiat parts of the two strips 89 and 10 may be spot-welded together. The lower strip 10 has a tab 13 struck out from the central part of the strip and bent down as shown. The terminal is inserted in the tapered hole in plate 8| from the right, the tab 13 bending up until it has "passed through the hole, when it snaps down and locks the terminal in the hole. The curved Jaws H and .12 are tensioned towards each other so I trunk unit by means of plates of insulating mathat they effectively grip the end of the line bar 88. V

It will be understood that there are 300 terminals carried on the five plates at the selection control unit. These terminals are in alignment with the 300 holes in the plates at the test unit of, the third vertical row, etc.

and with the corresponding holes in the plates at the trunk units.

The line and test bars are inserted in the switching mechanism from the left as seen in Figs. 1 and '2, or from the right as seen in Figs. 3 and 17. In the case of the line bar 68, for example, the end of the line bar is simply inserted in the upper left hand tapered hole 64 in plate 8|, Fig. 4, and is pushed through this hole and the corresponding tapered holes in the plates at the other trunk units and the test unit successively until finally it enters between the curved Jaws 'II and I2 of the corresponding terminal, as shown in Fig. 17. The other bars are inserted in the same manner. The bars can be just as read- 11? withdrawn and since they are interchangeable they need not be replaced in the same positions. It will be seen that each bar is supported at each trunk unit and at the test unit.

Thesubscribers lines may be connected to the line and test bar terminals by means of a 300- pair cable which is subdivided or formed at the end into 30 groups of conductors of i conductors each. The formed end of the cable is secured in a vertical position just outside the fanning strip I4, Fig. 3, and the 30 groups of conductors are passed through the 30 holes such as I5 in the fanning strip. The ten wires of each group are fanned out at the proper intervals for attachment to the ten terminals of the corresponding horizontal row. The arrangement follows the usual practice and will be readily understood.

The order in which the lines are connected to the terminals could logically be explained in connection with Fig. 6, but a considerable part of the terminals are covered up in this figure by other parts and accordingly Fig. 4 will be used for this purpose. Fig. 4 shows the ends of the in the first vertical row at the right, Fig. 4; the

lines of the second sub-group are connected to the bars of the second vertical row; the lines of the third sub-group are connected to the bars row the numbering is from top to bottom. Thus line II is connected to bars 16, I1 and I8, the two line conductors being connected to bars I6 and TI and the test conductor to bar I8; Line I2 is connected to bars I9, 80 and 8I, bars I9 and 88 being the line bars, While bar 8| is the test bar. The remaining lines in the first sub-group are connected in order to the remaining sets of bars in the first vertical row of bars. The lines in the other sub-groups are connected according to the same plan. .The foregoing describes the preferred arrangement, but other arrangements could be used.

The construction and arrangement of the intermediate trunks will next be explained. Each intermediate trunk consists of three separate and individually removable trunk elements, one trunk element for each conductor. One of these trunk elements is shown in Figs. 21 and 22. It comprises a metallic strip 82, preferably of phosphor In each vertical and test bars.

trunk elements.

bronze, having 11 integrally formed contact fingers such as 88 along one edge. The other edge .is embedded in a bar 88 ot molded plastic material such as Bakelite or polystyrene. This bar also has partially embedded in it a metallic strip 81 which may be of aluminum or brass or any suitable material. The trunk contact 84 with the integrally formed trunk terminal 85 is secured toone end of bar 88 by means of rivets, as indicated. The trunk contact is directly above the last or eleventh contact finger on strip 82. All the intermediate trunk elements are the same as the one described, except that the trunk terminals are made in three different lengths for convenience in connecting the trunk terminals at each trunk unit in multiple.-

The intermediate trunk elements are supported on the platesvsuch as 6 I which support the line The trunk'elements shown in Figs. 21 and 22, for example, assumed to be the upper. trunki element in Fig. 5, is assembled to plate 8| with the exposed portion of strip 81 in groove 65, the strip 81 and groove 85 serving to properly locate the trunk element on the plate. The cooperation of these parts will be clear from Fig. 23, which shows the upper trunk element in assembled position on plate 6 I There are 5 other trunk elements assembled on plate 6| in the same manner. The 6 trunk elements are held in position against plate 8| by the two spring clips 88 and 89. The spring clips 88 can be seen in Figs. 3, 5 and 23 and is secured to the vertical side member 28 of the trunk unit frame by screws 90 and 8| which are threaded into tapped holes 92 and 93, Fig. 7. The spring clip 38 has 6 rather stiff spring fingers which press the 6 intermediate trunk elements firmly against the plate BI. The spring clip 89 can be seen in Fig. 2 and is similar to spring clip 88.

Each of the other five plates such as 6| on the No. I tru'nk'unit also carries six intermediate Thereare therefore 30 of these intermediate trunk elements on the No. I trunk unit, all supported on the plates such a 8| in the manner described.

The strips such as 820i these trunk elements with thei integrally formed contact fingers such as 83 are the conductors of the intermediate trunks. There are 30 such conductors, or 10 intermediate trunks, each having two line conductors and a test conductor. The first and second strips 82, counting from the top down in Fig. 5, are the line conductors of the first intermediate trunk and the third strip 82 is the test conductor. The next three strip are the conductors of the second intermediate trunk, the next three strips constitute the third intermediate trunk, and so on.

It will be observed that the ten intermediate trunks are arranged in intersecting relation to the ten sub-groups of lines. The contact fingers such as 83 on the strips such as 82 of the intermediate trunks are in the same vertical rows as the line and test bars of the sub-groups of lines, and each contact finger 83 is associated with a particular line or test bar. These contact fingers constitute the circuit closing means whereby the ten lines of any sub-group may be connected, respectively, to the ten intermediate trunks.

Each intermediate trunk may be regarded as terminating in the three contact fingers at the left, Fig. 5, which are associated with the trunk contacts. The first intermediate trunk, for instance, terminates in contact fingers 94, 95 and 96 which are associated, respectively, with trunk contacts 84, 91 and 98. These trunk contacts have integrally formed trunk terminals 85, I and MI, respectively, which are connected in multiple with the corresponding trunk terminals of the other nine intermeditae trunks. The conductors of the outgoing trunkline which is individual to the No. I trunk unit may be connected to the trunk terminals associated with the last inter-- mediate trunk, or at any other point on the multiple. It will be understood f cm the' foregoing that the contact fingers such a 94, 95, 96,-etc., in

which the intermediate trunks terminate, constitu'te the circuit-closing mean whereby any intermediate trunk may be connected to the outgoing trunk line.

The multiple connections between the trunk terminals are not shown in Fig.5 but may be made with bare wire 'in known manner. The connections are shown in the circuit drawing, Fig. 37.

The arrangement of the intermediate trunks and trunk terminals at each of the other trunk units is the same as described for theNo. I trunk unit.

The arrangement at the test unit is somewhat different, in that only the trunk elements associated with the test bars are furnished. as indicated in Fig. 17. Furthermore. at each trunk element the eleventh contact finger, or the contact finger associated with the trunk contact, is bent up and permanently soldered to the trunk contact. The ten trunk terminals are not multipled together, but are included in individual test cir ,parts.

The operating mechanism at the No. I trunk unit will next be described. Thi mechanism comprises an operating magnet, ten so-called tens actuators, each adapted to connect a sub-group of ten lines to the ten intermediate trunks, and ten units actuators, each adapted to connect an intermediate trunk to the outgoing trunk line. The connections are established by selectively opcrating the contact fingers of the intermediate trunks.

The trunk operating magnet comprising wind-- ing 29, core 28, and pole pieces 30 and 3| has already been described with reference to Fig. 7. The magnet armature is indicated at I02 and is carried on a pivoted yoke which comprises a horizontal member I03 and has two integrally formed downwardly sloping members I04 and I05, having ears I06 and I01, respectively. The pivots for the armature yoke are the-shoulder screws I08 and I09 which pass through slots in the frame extensions 28 and 21, respectively, and are'threaded into tapped holes in the ears I06 and, I01, respectively. The two pivot screws have round heads which rotate in circular recesses in the frame extensions.

The horizontal member I03 of the operating magnet armature'yoke carries ten lifting pins such as I I0 for operating the tens actuators. The lifting pins are rigidly secured to the armature yoke, having a drive fit in holes in the horizontal member I03. The horizontal member I03 also has an integrally formed extension comprising a I downwardly extending member I20 and a slotted horizontal member I2I fo operating the lifting rod for the units actuators.

One of the tens actuators is shown in Figs. 24

and 25. It comprises a metallicbar III of rectangular cross-section, and live molded members such as 2, each having six projecting pins such as 0. The molded members II2 are slotted along one edge to receive the bar III towhich they are secured by rivets such as I II. The pins H3 are equally spaced and the spacing is the same as the vertical spacing of the contact fingers of the intermediate trunks. At the top the tens actuator bar III carries a molded clutch housing I I5, as can be seen in Fig. 5. The clutch housing may be molded on the bar III, to which it is rigidly attached.

The tens actuator bar III is held in position at the top by the lifting pin IIO which passes down into the clutch housing I I0. At the bottom the bar is vertically slidablc v in a rectangular opening in the plate I I8 which is closed by a plate Ill secured to plate H0 in suitable manner as by spot welding. The plate H0 is supported in slots which are formed in the foot members 24 and-25 of the trunk unit frame and is retained in the slots by set screws H0 .and H9. The bottom of bar III rests on plate I." which supports the weight of the complete tens actuator including the clutch housing H5. 4

- It willbe seen from Fig. 5 tact fingers which serve to connect the. ten intermediate trunks to the ten lines of the first subgroup rest on the thirty pins such as II3 of the tens actuator I I I. It will be clear, therefore, that that the thirty cona longitudinal movement of the tens actuator in an upward direction will be effective to connect the ten lines of the sub-group to the ten intermediate trunks, respectively, by moving the contact fingers into engagement with the associated line and test bars.

It will also be seen from Fig. 5 that the No. I trunk unit is provided with ten tens actuators altogether, or nine in addition to the one which has been described. These tens actuators are all the same and are associated, respectively, with the ten sub-groups of lines.

The remaining trunk units are equipped with tens actuators like the No. I trunk unit. The same is true of the test unit. Although in the test unit connections are made only to the test bars, the same type of tens actuator may be used.

One of the units actuators is indicated at I22 in "Figs. 2 and 5 and is shown in detail in Figs. 26, 2'1

and 28. It may be molded 01' a suitable plastic material and comprises a clutch housing I22 having an extension I23 which carries three actuator pins I24, I25 and I26. The clutch housing part of the units actuator has a longitudinal bore for receiving the units actuator lifting rod I21, and contains a spring clutch which will be described presently.

the trunk unit frame. The guide is attached to the frame at the top by means of a screw I30, as seen in Figs. 2 and 5. The said screw also-supports one end of the tens selector rod guide I, to be presently described. It passes through a hole in member I29 of the units actuator guide and a hole in the selector rod guide, and is threadedintoa tapped hole in the frame, At the bottom "the member I29 of the units actuator guide is provided with an offset portion I32 having an ear I33 which rests against the side of foot member The member I28 of the units actuator guide is provided with ten slots such as I35, Fig. 27, for receiving the extensions I23 of the ten units actuators. In the case of the units actuator I22, for example, it will be seen that the housing I22 is on one side of the slotted member I20. while the pins such as I24 are on the other side, the extension I23 lying in the slot I35. The actuator is supported. by engagement of the extension I23 .with the bottom of the slot I35. This slot is somewhat longer than the extension I 23 of the actuator, which permits an upward movement of the actuator.

The units actuators are retained in position by means of the lifting rod I21, which passes verthe tens actuator and a similar upward movement of the lifting rod I2I associated with the units actuators. The lifting pins such as IIO move freely in the clutch housingssueh jas II5, leaving the associated tens actuators unoperated. except for one particular tens actuator where the spring clutch in the associated clutch housing has been operated. This particular ten actuator, and it may be any one of the ten, is temporarily coupled to the associated 'lifti'ng pinby/the spring tically through all the units actuators, as seen The extension I carries a horizontal part I2I which is slotted at the rear to receive the lifting rod I21. The lifting rod is moved longitudinally upward by means of a washer I38 which rests on top of the slotted member I2! and is prevented I from sliding upward on the lifting rod by a pin I31. A little higher up on the lifting rod 9. similar pin and washer are provided. The spring I38, compressed between the last mentioned washer and the extension 21, is the restoring spring for the lifting rod.

The upward movement of lifting rod IN is effective to operate the contact springs 31!! and 383, which with their associated .contact springs are suitably mounted at the top of extensions 26 and 21.

It will be understood now that the ten units actuators are individual, respectively, to the ten intermediate trunks and that each units actuator is adapted to connect its associated intermediate trunk to the outgoing trunk for the No. I trunk unit. In the case of the units actuator I22, for example, which is the second units actuator from the top, Fig. 5, the pins I24, I25 and I25 support the eleventh or terminal contact fingers of the second intermediate trunk and are adapted to move said contact fingers into engagement with the associated trunk contactswhen the units actuator is moved upward by the lifting rod I 27.

Each of the other trunk units is provided with ten units actuators, the same a the No. l trunk unit being described. The test unit, however, has no um'ts actuators. As previously explained, the eleventh contact finger of each trunk element in the test unitis permanently soldered to the associated trunk contact, so-called, and consequently no units actuators are required.

From the description up to this point it will be understood that the No. 1 trunk unit, which is representative of the other trunk units and of the test unit with the exceptions noted. is provided with an operating magnet 29 the energization of which iseifective through the medium of the armature I02 and armature yoke I03 to produce a longitudinal upward movement of the ten lifting pins such as IIO which are associated with clutch and is moved longitudinally upward by the lifting pin. Likewise the lifting rod I21 moves freely upward through all the units actuators except in the case of one particular units actuator where the spring clutch has been operated.

Thus it will be seen that the operation of the trunk magnet i effective to operate one tens actuator and one units actuator. The actuators are operated by means of the associated spring clutches whereby they are coupled one to a lifting pin such as I I0 and the other to the lifting rod I21. These spring clutches will be described,

but first it will be desirableto describe the selecting bars by means of which the spring clutches are selectively operated.

There are ten tens selecting bars and ten units selecting bars. The tens selecting bars extend through and are common to all the trunk units and the test unit. The units selecting bars also are common to all the trunk units. They extend through or rather past the test unit but perform no function at the test unit.

'One of the tens selecting bars is indicated at I40, Figs. 2 and 5, and is also partially shown in Figs. 29 and 30. It is a metal bar, of rectangular cross-section, the length of which depends on the trunk capacity of the switching mechanism. The bar I40 is provided with a plurality of rectangular openings such'as I, one at each trunk unit and one at the test unit. The other nine tens selecting bars are the same as bar I40. While the ten tens selecting-bars are all alike where they pass through the trunk units and the test unit, as stated, there is a difl'erence in the length of the bar sections extending between the test unit I and the selection control unit, which makes five of the bars somewhat longer than the other five. This is due to the staggered mounting of the magnetic clutches which couple the tens selector bars to the armature yoke of the common operating magnet, as will appear hereinafter.

The tens selector bars are supported at each trunk unit and at the test unit by means of a. tens selector bar guide. In the case of the No. 1 trunk unit the tens selector bar guide is indicated at I34, Figs. 2 and 5. At one end the guide I34 is secured to the trunk unit frame by the same screw I30 that holds the upper end of the units actuator guide, as previously mentioned. At the other end the guide I34 is secured to the trunk unit frame by means of a screw I42. Th guide I34 may be made of suitable plastic material molded orcut in the desired shape, as shown, and is provided with ten tapered openings such as I43 for receiving the ten tens selector bars. The selector bars are freely slidable in these openings.

One of the units selector bars is indicated at I44, Figs. 2 and 5, and is also partially shown in Figs. 26, 27 and 28.- The selector bar I 44 is a metal bar of rectangular cross-section, and is generally 74 Theunits selector-bars are supported at each aseaorr trunk unit b means of a units selector bar guide. In the case of the No. I trunk unit the units selector bar guide is indicated at I48, Figs. 2 and 5. The guide I45 may be of molded plastic material, like the tens selector bar guide I34, and i secured to the member I29 of the units actuator guide by means of countersunk screws, as indicated in Fig. 28. The guide I46 is provided with ten tapered openings such as I41 for receiving the units selector bars. The units selector bars are not neces; sarily supported at the test unit, but a units actuator guide and selector rod guide may be supplied at this unit if desired.

It will be convenient now to describe the.spring clutches hereinbefore referred to as being provided for coupling the units actuators to-the lifting rod I21 and for coupling the tens actuators to the associated lifting pins such as IIO.

One of the units actuators with its spring clutch is shown complete in Figs. 26, 2'7 and 28. The units actuator has already been described. The spring clutch comprises a spring having a plurality of coils I50 which are located in a recess II in the clutch housing I 22 of the units actuator and surround the lifting rod I21. At the lower end the spring has a straight section I52, Fig. 28,

bearing against the inside of the clutch housing. and a straight section I 53, bent at rightangles to section I52, which extends across the opening in the clutch housing and bears against the edge I54 thereof. The straight sections I52 and I53 serve to anchor the spring and prevent rotation of the lower end thereof relative to the clutch housing in either direction. The last coil of the spring at the top terminates in a straight section I55 which extends outside the clutch housing through a slot I56. The section I55. of the spring is long enough so-that it extends a short distance through theopening I45 in the units selector bar It maybe mentioned that the selector bar I44 is shown in operated'position in all three of Figs. 26. 27 and 28.

The member I 29 of the units actuator guide is provided with a plurality of integrally formed clutch locking cams, one for each of the units The clutch locking cam associatedactuators. with the units actuator I22 is indicated at I51, Fig. 2. and is also shown in Figs. 26, 2'7 and 28. The cam I51 extends to the right from member I29, as seen in Figs. 26 and 28 and its extremity is approximately in line with section I55 of the clutch spring when the latter is in operated position. The location of the cam I51 vertically is such that its lower edge is just above and in light contact with the spring section I55 when the latter is in its normal or unoperated position, as shown by dotted lines in Fig. 28. The described relation between the cam I51 and spring section I55 will be clear from the drawings.

' When'the spring clutch is not operated, that is, when the spring section I55 is in its dotted line position, the coils I50 fltloosely around the lifting rod I21, which is freely slidable through the said coils. It will be understood, therefore, that if the lifting rod I21 is upward by the operation of e trunk operating magnet 29 at a time when the selector bar I44 therewith.

is in normal'position the units actuator I22 will not be affected. It should be noted furthermore that since in the normal position of the selector bar I44 the spring section I55 is directly beneath the locking cam I51, the said spring section and cam will positively prevent any upward movement of the units actuator which might otherwise occur due to friction between the lifting rod and the clutch housing or between the lifting rod and the coils I50 of the clutch spring.

Ifthe lifting rod I21 is moved longitudinally upward at a time when the selector bar I44 is in operated position, as shown in Fig. 26, for example,- the coils I50 of the clutch spring will have been tightened on the lifting rod, as previously "described. The said coils will grip the lifting rod, and the, units actuator will move upward During this movement of the units actuator the spring section I55 slides upward in the rectangular opening I45 in the selector bar I44 to a position near the upper left hand corner of this opening, as seen in Fig. 26. The width of the opening I45 should be somewhat greater than the distance through'which the units actuator moves. As regards the adjustment of the selector bar, Fig. 26 shows that when the selector bar is in operated position the rear end of opening I45 is exactly in line with the end of locking cam I51. The adjustment is not critical, however. The selector bar may move somewhat fartheito the right, in which case the spring section I55 will merely bend a little after the coils I are'fully tightened on the lifting rod. or the selector bar may not fully reach the position in which it is shown in Fig. 26. in which case the spring section I will slide upward along the end of cam I51 during the upward movement of the units actuator. The lower corner of the cam is rounded off to facilitate this action. In any event after the upward movement of the units actuator has taken place the spring section I55 will be a substantial distance above the lower edge of cam I51 and when the selector bar I 44 is released the spring section I55 is prevented from restoring, due to its engagement with the end of the cam. Thus the cam I51 locks the spring clutch in operated position and holds it operated comes fully restored, the spring section I55 clears the end of the cam and the spring clutch is released.

The remaining nine units actuators on the No. 1 trunk unit with their spring clutches are constructed the same and operate the same as the units actuator I22 just described, except that the spring clutches are operated by different selector bars. There are ten units selector bars, as prevously. mentioned, which operate the spring oved longitudinally clutches in the ten units actuators, respectively, at the No. 1 trunk unit. These selector bars, moreover are common to all the trunl: units and when any selector bar is operated to operate the spring clutch in the associated units actuator at the No. 1 trunk. unit it simultaneously operates the spring clutches in the corresponding units actuators at all the other trunk units. 

